> "Objects respond to messages from "god" at arbitrary times in an untestable way."

Not untestable or arbitrary, or necessarily a problem. First, almost all processes have some structure that is not random and arbitrary. Second, the science and engineering of distributed systems has some results and approaches that help deal with events that are, or appear, arbitrary. For example idempotence, immutability, monotonically increasing functions such as max() that give the same result independent of the timing or order of events. It's not easy necessarily, but in a distributed system, events are what you have under the pile of turtles.